Fiber-to-the-premises (FTTP) from local telephone and cable service providers is rapidly being implemented. This service requires a broadband optical fiber distribution network comprising local optical fiber distribution cables that are installed in neighborhood and city streets. The local distribution cable is a large fiber count (multi-fiber) cable. Single fiber or few fiber cables are used for the “drop” line from the street to the premises. In many cases, aerial drop lines are used, and these have special requirements. In other cases, buried drop lines are used, and these have different specific requirements.
Optical fiber drop cables are made in several designs. Most of these designs mimic earlier copper cable versions. Physical resemblance is deliberate, so that the external cable appearance matches that of existing copper versions, and standard hardware and installation equipment may be used for both. Thus “A-drop” optical fiber cable is an optical fiber version of A-drop copper cable, and is made in the same flat or ribbon-like configuration. Aerial drop cable typically has one or more strength members for support. A common A-drop or flat cable design comprises one or more optical fibers between two strength members. See for example, U.S. Pat. No. 6,501,888.
Optical fiber cables also commonly contain gel-filling compounds for preventing water excursion in the cable. When water enters a cable, flow of water along the length of the cable is blocked by the gel. However, gel filled cables are time consuming to install and repair, as the gel must be completely removed from the optical fiber prior to splicing operations. Moreover, since the drop wire is typically attached to the side of a customer's home or building, bleeding of ingredients in the cable onto the customer's building may cause cosmetic or other problems.
Since aerial drop cables are subjected to considerable movement and sag due to wind and ice build-up, and due to mechanical strain caused by differential thermal expansion, aerial drop cables commonly have a loose fiber design. In this design the optical fibers are loosely received, “floating” within the cable encasement. The premise is that the optical fibers are mechanically isolated from at least some of this movement. However, a drawback to this design is that the cable may suffer fiber retraction due to the movement just mentioned. Fiber retraction occurs when the outer sleeve of the optical fiber cable sags or is stretched relative to the optical fibers. Excessive fiber retraction may result in damage or breakage of the fibers.
Several examples of drop cable are described in U.S. Pat. No. 4,761,053. Most of these examples describe copper drop wire but a few optical fiber versions are given as well. These show loose fiber designs as just mentioned.
Another FTTP drop cable design is shown at pages 500–506 of the Proceedings of the 51st International Wire and Cable Symposium. This design is a combined flat optical fiber cable and a wire support member.
New designs offering for FTTP drop cable that offer compact size and low cost are continually being sought.